Posted
by
Unknown Lamer
on Monday April 09, 2012 @09:09PM
from the the-emperor's-graphene-clothes dept.

slew writes "Looking at liquids with a transmission electron microscope to observe things like crystal growth has been difficult to do. This is because liquids need to be confined to a capsule to view them in a TEM (because the electrons are flying at the sample in a chamber near vaccuum pressures where liquids would evaporate or sublimate). Traditional capsules of Silicon Oxide or Silicon Nitride have been fairly opaque. A paper describes a new technique with a 'pocket' created between two graphene layers which can hold liquids for observation by a TEM and the graphene is apparently much more transparent than previous materials allowing a better view of the processes (like crystalization), taking place in the liquid. The BBC has a non-paywalled summary article."

tl;dr, liquids have to be confined to be scanned in an electron microscope because otherwise they'll evaporate due to the near-vacuum pressures, previous solutions confined them in capsules that were not so transparent, new solution uses more-transparent bubbles between graphene layers to trap liquids in

TFA seems inconsistent with a recent report that graphene is so transparent to water than one can in effect use a graphene barrier to selectively out-diffuse water. (http://biology-forums.com/index.php?topic=18349.0;topicseen) gives a popularized account of the original work that indicates you can concentrate alcohol in alcohol/water solutions by simply putting a graphene film bottlecap on the bottle. Yahoo! for those of us who want to make EverClear from vodka, I guess.

So if this story is talking about using graphene to enable TEM examination of aqueous systems, I don't see why the water doesn't diffuse rapidly out of the graphene bubble boundary, especially given the tiny volumes that would be involved in a TEM specimen.

The graphene water diffusion paper is "Unimpeded Permeation of Water Through Helium-LeakTight Graphene-Based Membranes", paywalled at Science Mag. Really interesting.

I think this is a non-aqueous system. I don't have access to this paper, but in an earlier paper [osti.gov] from the same group (using a silicon nitride cell) mentions that a "stock solution for synthesis was prepared by dissolving Pt(acetylacetonate)2 (10 mg/mL)
in a mixture of o-dichlorobenzene and oleylamine (9:1 in volume ratio). About 100 nanoliters of the growth solution was loaded into the reservoir of a liquid cell and the
solution was drawn into the cell by capillary force."

1) As others have said, this system is non aqueous (Pt(acac)2 in o-dichlorobenzene and oleylamine).2) The graphene-as-water-filter was actually graphite oxide, which has a lot of functional groups protruding out from the basal planes into the interstices between layers. It's also still pretty unclear how the diffusion was happening at all, given that helium couldn't even wend its way through the interstitial galleries of the graphite oxide paper.

What I recall from reading the graphene/water selectively permeable barrier paper (Nair et al. in Geim's research group, Science 335, 442-444 (2012)), makes the situations not comparable. The graphene in the selectively permeable barrier was not a monolayer as in this topic's paper, but rather a sort of graphene baklava: stacked monolayers with more-or-less random holes/gaps in each layer (and the graphene was oxidized). The authors offered a nanocapillary model where "a network of graphene nanocapillaries formed within GO laminates, which are filled with monolayer water under ambient conditions." Water and graphene each are extraordinary materials; put them together and things get even more extraordinary.

This post is the top thing on google when searching for "graphene baklava"! The rest seems to be blogs about baklava using the graphene wordpress template... At least I was able to discover what a baklava is.

Seriously though is anyone else thinking graphene is the next massive step in science? Hardly a week goes by without hearing about some fantastic achievement graphene related such as creating 3 atom thick glass, filtering pure H2O, improving charge density in batteries, converting photons to electrons, and best of all it can be made from cookies! [slashdot.org]